Hot melt adhesive metered dispensing systems must be operated intermittently in order to, for example, only deposit the hot melt adhesive material upon predetermined regions of substrates, at predetermined times, so as not to cause operational problems or to result in undesirable product characteristics, and concomitantly, to control the flow of the hot melt adhesive material during those periods of time when the hot melt adhesive material is not actually being dispensed. Control modules, having suitable valve mechanisms incorporated therein, are conventionally used to effectively control the starting and stopping of the flow of the hot melt adhesive material to the dispensing nozzle and its associated discharge orifice. In view of the fact that the metering pumps, for supplying the hot melt adhesive material to the control module, are typically operated in a continuous manner for achieving proper or desirable operational and control parameters, the hot melt adhesive material must therefore be effectively re-routed during those periods of time that the hot melt adhesive material is not actually being conducted to the dispensing nozzle block and its discharge orifice. This has been conventionally achieved by means of the control module which is effectively provided with two outlet ports whereby the hot melt adhesive material can alternatively be delivered to the dispensing nozzle block and its discharge orifice or to a recirculation passage or circuit.
In connection with the fluid flow of the hot melt adhesive material through the recirculation passage, it is necessary to control the backpressure within the recirculation passage such that the backpressure within the recirculation passage will be similar to, correspond with, or effectively match the fluid pressure characteristic of the hot melt adhesive material which is being conducted through the supply passage leading to the dispensing nozzle block and its discharge orifice. As a result of the control of the backpressure within the recirculation passage, when compared to the fluid pressure characteristic of the hot melt adhesive material which is being conducted through the supply passage leading to the dispensing nozzle block and its discharge orifice, it is therefore possible to effectively minimize pressure spikes within the system and therefore eliminate significant variations in the amount of hot melt adhesive material which is actually dispensed from the discharge orifice of the dispensing nozzle block. In other words, problems in connection with the discharge of too much or too little hot melt adhesive material from the discharge orifice of the dispensing nozzle block are effectively prevented or eliminated. The actual control of the backpressure within the recirculation passage is conventionally achieved by means of a suitable simple fixed orifice which is located at a predetermined location within the recirculation passage, that is, somewhere along the recirculation flow path.
Conventionally, the fixed orifice has been placed within the recirculation passage, or along the recirculation flow path, at a position which is located between the applicator and the control module, and external of the dispensing nozzle block. In view of the fact, however, that the fixed orifice must effectively be matched with the size or configuration of the dispensing nozzle block and its discharge orifice, in order to achieve essentially the same fluid pressure within both the recirculation passage and the supply passage leading to the dispensing nozzle block and its discharge orifice, the provision of the fixed orifice at its conventional location, that is, between the applicator and the control module, and external of the dispensing nozzle block, becomes problematic when the particular dispensing nozzle block and its discharge orifice are changed or replaced with a dispensing nozzle block and a discharge orifice having, for example, a different design, in order to, for example, achieve a different hot melt adhesive deposition or distribution pattern, because operational personnel must then likewise replace the fixed orifice. Not only does this process require the operational personnel to implement additional setup procedures, but there is the potential or possibility of operational personnel mismatching the fixed orifice with the dispensing nozzle block and its discharge orifice.
Accordingly, there is a need in the art for a new and improved hot melt adhesive material dispensing system wherein the recirculation of the hot melt adhesive material, during those time periods of time that the hot melt adhesive material is not actually being conducted to the dispensing nozzle block and its discharge orifice, would be implemented without encountering the aforenoted operational problems characteristic of conventional hot melt adhesive dispensing systems.